The following description is provided to assist the understanding of the reader. None of the information provided or references cited is admitted to be prior art.
Bisphenols constitute a family of compounds, which includes many substances that have as a common chemical structure two phenolic rings joined together through a bridging carbon. Various bisphenols and their derivatives have been synthesized and evaluated for use in a variety of industrial products, including polymers. Since these compounds are very widely used in industry, particularly in plastics, potential exposure of human beings to them is becoming a significant point of discussion. Some have expressed concern because bisphenols exhibit endocrine-disrupting activity, in which they mimic or antagonize the biological functions of natural hormones. Because of this, their use in several consumer products, such as, e.g., linings for food and beverage cans can be problematic. These linings may permit bisphenols, such as Bisphenol-A (2,2-bis(4-hydroxyphenyl) propane; BPA), to migrate into the food and beverage contents, placing consumers directly in harm's way through BPA's potential effect on development of the male reproductive system, similarities with the known human carcinogen and teratogen, diethylstilbestrol, estrogenic effects on animals in the ecosystem, and many other negative effects.
Previously proposed solutions such as non-BPA-containing coatings and dual-layer BPA-barrier coatings are associated drawbacks such as, e.g., lack of coating efficacy and poor integration into existing canning processes. Further, proposed alternatives, such as single-layer replacement linings, suffer from disadvantages such as flavor contamination, inability to withstand retorting temperatures, the need for sterilization, insufficient flexibility for processing, and lack of chemical resistance. Proposed double layer linings involve comparatively elaborate processing and are, therefore, prohibitively expensive. Moreover, any proposed replacement lining may have unanticipated issues simply due to a lack of the decades of experience and process improvement known for existing linings. In essence, existing linings are far superior to other proposed linings in many different respects and suffer only from the presence of BPA. Therefore, a desirable method for reducing BPA migration from can linings is cheap, effective, food-safe, and easily integrated into the canning process, and at the same time, matches or preserves the many advantages of existing linings.